In oil and gas drilling operations, it is universally known that the drill bit is mounted at the end of a drill string which extends from the bottom of the hole being drilled up to a drilling rig. Typically, the drill string extends through a rotary table which includes the equipment for rotating the drill string and thereby rotating the drill bit at the bottom of the drill string in order to drill the hole.
Basically, there are three types of drill pipe components that can be used in a drill string. The most common type of drill pipe is known by that name and basically comprises elongated tubular pieces having a "pin" or male thread at one end and a "box" or female thread at the other end. Such standard drill pipe is typically 31 feet long and has a uniform wall thickness in a range of 0.25-0.50 inches. Another type of drill pipe is known as the "drill collar". Drill collars are much heavier than drill pipe and are typically located near the bottom of the hole. Drill collars are typically attached between the bottom of the standard drill pipe part of the drill string and the drill bit itself. Drill collars typically have a greater wall thickness than standard drill pipe and generally operate in a manner to provide weight to the bottom of the drill string to urge the drill bit downwardly.
The third form of drill pipe is known as "heavy wall drill pipe". Typically, heavy wall drill pipe is approximately 31 feet in length and includes upset end portions forming pin and box threaded connections and further has a central protector of larger diameter than the central elongated body section. U.S. Pat. Nos. 3,784,238 and 3,773,359 disclose heavy wall drill pipe or intermediate drill stem having an elongated tubular steel body terminating at either end in connectors of larger diameter and further having an intermediate protector of larger diameter located intermediately between the ends of the elongated tubular steel body. Typically, such intermediate drill stem is approximately 31 feet in length and has in its central section of uniform diameter a thickness of at least 5/8 inch. Central protectors or sections of raised or larger diameter are not wholly unique to heavy wall drill pipe. U.S. Pat. Nos. 3,484,122 and 3,458,922 disclose standard drill pipe having central protector sections.
Typically, heavy wall drill pipe is manufactured from worn out drill collars by machining the drill collar down in its central section to a section of small diameter leaving a central protector and upsets on the ends. Heavy wall drill pipe can also be manufactured using tubing which can also be turned down on the ends leaving a central protector. The upset ends for the connectors are then welded on. U.S. Pat. Nos. 3,784,238 and 3,773,359 disclose methods of manufacture of heavy wall drill pipe or intermediate drill stem. Manufacture of heavy wall drill pipe from a single piece of tubing by machining is quite undesirable from an economic standpoint due to the tremendous waste of material and machine time. Therefore, most heavy wall drill pipe has been manufactured from tubes or pipes with connector portions being added to each end. The utilization of welded on connector portions has generally been satisfactory; however, it is believed that it would be more desirable from an economical and practical standpoint to manufacture heavy wall drill pipe from an integrally formed bar.